Capillary-Channel Probes For Liquid Pickup, Transportation And Dispense Using Stressy Metal

ABSTRACT

Fluidic conduits, which can be used in microarraying systems, dip pen nanolithography systems, fluidic circuits, and microfluidic systems, are disclosed that use channel spring probes that include at least one capillary channel. Formed from spring beams (e.g., stressy metal beams) that curve away from the substrate when released, channels can either be integrated into the spring beams or formed on the spring beams. Capillary forces produced by the narrow channels allow liquid to be gathered, held, and dispensed by the channel spring probes. Because the channel spring beams can be produced using conventional semiconductor processes, significant design flexibility and cost efficiencies can be achieved.

RELATED APPLICATIONS

This application is a divisional of 10/213,059, entitled“Capillary-Channel Probes For Liquid Pickup, Transportation And DispenseUsing Stressy Metal” filed Aug. 5, 2002, now U.S. Pat. No. 7,241,420.

FIELD OF THE INVENTION

This invention relates generally to microfluidic devices, and moreparticularly to liquid handling probes for such devices.

BACKGROUND OF THE INVENTION

The developing field of microfluidics deals with the manipulation andmeasurement of exceedingly small liquid volumes currently down to thenanoliter, or even picoliter range. For example, modern analyticalintegrated circuits (ICs), such as “system on a chip” (SOC) or “lab on achip” (LOC) biochips, can analyze solutions that are deposited directlyon the chip surface. Typically, the surface of an analytical IC willinclude an array of analysis locations so that multiple analyses can beperformed simultaneously. A “microarraying” system that includes abiochip is extremely useful for genetics research because of thesubstantial improvements in efficiency provided by this parallelanalysis capability. To maximize the number of analysis locations (andtherefore the number of analyses that can be performed at one time), thesize of each analysis location on the biochip is minimized. To ensurethat the biological solution from one analysis location does not flowinto a different analysis location, an array (often referred to as a“microarray”) of microfluidic “printing tips” is used to dispense aprecise volume of the biological solution at each analysis location.

FIG. 1 is a perspective view of a conventional microarraying system 100,which includes a stage 110 for supporting a biochip 120, a microarray130 mounted to an XYZ positioning subsystem 160, and acomputer/workstation 170 that serves as both a system controller and ameasurement data processor. Microarray 130 includes a plurality ofprinting tips 150 mounted in an array formation on a mounting base 140.XYZ positioning subsystem 160 moves microarray 130 in response tocontrol signals provided by computer/workstation 170 to collect anddispense samples of test solutions in an array pattern on biochip 120. Achannel 151 cut into the end of each printing tip 150 stores anddispenses tiny samples of the test solutions onto specific analysislocations on biochip 120. In this manner, each printing tip 150 acts asa microfluidic conduit—i.e., a transport pathway for microfluidicvolumes of liquid. Biochip 120 then analyzes the samples in parallel andprovides the results to computer/workstation 170 for further processing.As mentioned previously, this type of concurrent analysis greatlyreduces the amount of time required to perform a set of experiments.

To ensure that test samples are accurately and evenly placed on biochip120, printing tips 150 in microarray 130 must be made to extremely tighttolerances and must be precisely arranged in microarray 130. As thenumber of pins is increased to allow larger numbers of samples to beconcurrently tested, the dimensional requirements only become stricter.As a result, the microarrays used in conventional microarraying systemsare expensive and difficult to manufacture. For example, companies suchas Oxford Lasers, Ltd. manufacture the metal pins used to dispensebiological solutions in microarraying systems such as microarrayingsystem 100 using techniques such as electro-discharge machining (EDM)and copper-vapor-laser (CVL) micro-machining. The minimum channel widthin such pins is roughly 10 μm, with each pin being fabricatedindividually and taking up to 30 minutes to complete. Once pin formationis complete, the pins still must be assembled into the high-precisionmicroarray, which adds additional time and expense to the manufacturingprocess. This low production throughput (Oxford Lasers, Ltd. iscurrently manufacturing about 1000 pins/months for BioRobotics) meansthat the final microarrays are extremely expensive. This in turn impactstesting throughput, since the high cost of the microarrays mandates thatthey be reused rather than replaced. Therefore, to preventcross-contamination, the microarrays must be meticulously cleaned, whichcan be very time-consuming.

Even for microfluidic systems using a smaller number of printing tips,pin costs can be problematic. For example, FIG. 2 shows a perspectiveview of a dip pen nanolithography (DPN) system 200. DPN system 200includes a stage 210 for supporting a wafer 220, a micropen assembly 230mounted to an XYZ positioning subsystem 260, and a computer/workstation270 that serves as a system controller. Micropen assembly 230 includes aprinting tip 250 mounted in a mounting base 240. XYZ positioningsubsystem 260 moves micropen assembly 230 in response to control signalsprovided by computer/workstation 270 to print a desired pattern on wafer220. A channel 251 is cut into printing tip 250 to allow the printingtip to act as a microfluidic conduit and apply a print solution ontowafer 220. This type of micropen-based lithography can allow morecomplex and detailed patterns to be printed than would be possible usingconventional lithography techniques. However, as with microarrayingsystems, the difficulties in fabrication and the high cost associatedwith the metal pins used in micropen assemblies limit the usefulness ofcurrent DPN systems, for much the same reasons as were previouslydescribed with respect to conventional microarraying systems.Alternative DPN systems, such as the lithographically-formed planarbeams with perpendicular printing tips is described in “A MEMSNanoplotter with High-Density Parallel Dip-Pen Nanolithography ProbeArrays”, Zhang et al., Nanotechnology, v13 (2002), pp. 212-217, presentother difficulties, as the flat configuration of the planar beams canconsume significant die area, thereby limiting the printing tip density,and the printing tips themselves require delicate sharpening operationsthat can adversely impact both yield and cost.

What is needed is a microfluidic conduit that can be produced and formedinto microfluidic devices such as microarrays and micropen assemblieswithout the manufacturing difficulties and high costs associated withconventional metal pins.

SUMMARY OF THE INVENTION

The present invention is directed towards fluidic systems that areformed using stress-engineered spring material (e.g., “stressy metal”)films. The spring material films are formed into channel spring probes,each of which includes a spring beam having a fixed end (anchor portion)attached to a substrate and a free section bending away from thesubstrate, and a channel or multiple channels in or on each spring beam,parallel to the curvature of the spring beam. The channel(s) in and/oron the spring beam allow the channel spring probe to act as a fluidicconduit. The channel and tip configurations (referred to in theaggregate as “fluid handling features”) of the channel spring probe canbe designed to enhance the ability of the channel spring probe to store,draw fluid into, or dispense fluid from the channel(s). A channel springprobe or multiple channel spring probes can be used in any systemrequiring a fluidic conduit that provides out-of-plane fluid handlingcapabilities; e.g., a microarraying system, a DPN system, or a fluidiccircuit.

Channel spring probes of the present invention are produced by forming(e.g., sputtering, chemical vapor deposition, or electroplating) aspring material (e.g., metal, silicon, nitride, or oxide) onto asubstrate while varying the process parameters (e.g., pressure,temperature, and applied bias) such that a stress-engineered springmaterial film is formed with an internal stress gradient in the growthdirection (i.e., normal to the substrate). The spring material film isthen etched to form an elongated island of spring material, and ananchor portion (fixed end) of the spring material island is then masked.The unmasked portion of the spring material island is then “released” byremoving (etching) a sacrificial material located under the unmaskedportion, forming a spring beam curving away from the substrate. In oneembodiment, the sacrificial material removed during the release processis a separate “release” material layer (e.g., Si, SiNx, SiOx, or Ti)that is formed between the substrate surface and the spring materialfilm. In another embodiment, the spring material film is formed directlyon the substrate (e.g., silicon or quartz), and the substrate itself isetched during the release process. The released portion of the springbeam bends away from the substrate as the internal stress gradient ofthe spring material film relaxes, while the anchor portion remainssecured to the substrate. By controlling the internal stress gradient ofthe spring material film, along with other spring beam characteristics(e.g., thickness, length, etc.), a desired curvature can be achieved.

According to another embodiment of the invention, a substrate is coatedwith resist and patterned to define the channel spring probe area. Amaterial stack (including release layer and spring material film) isthen deposited over the entire substrate. A lift-off step (e.g.,submersion in acetone and applied ultrasonic agitation) is then used toremove the material outside the channel spring probe area. The advantageof the lift-off process is that it works with nearly any springmaterial, whereas the etching process allows only for spring materialsthat etch well.

Note that according to an embodiment of the invention, fluid handlingfeatures can be formed directly in the original spring material island,so that once the free portion is released from the substrate, thedesired fluid handling features are already incorporated into the springbeam. In such a case, the channel spring probe is defined by the springbeam itself. Alternatively, the spring beam can be formed “blank” (i.e.,having no integrated fluid handling features), with additionalprocessing used to form channel structures on the surface(s) of thespring beam. In this case, the channel spring probe includes both thespring beam and the additional channel structures. Note that theadditional processing operations that foam the channel structures can beperformed either before or after release of the free portion of thespring material island from the substrate.

The channel spring probes of the present invention provide severaladvantages over conventional metal pins. For example, dispensingassemblies, such as microarrays or micropen assemblies, made usingspring material technology can be manufactured much more cheaply thantheir conventional counterparts, since thousands of channel springprobes can be manufactured simultaneously using common fabricationmethods such as lithography, sputtering and plating (versus metal pinsthat must be individually produced).

Furthermore, the channel spring probes can be formed in the desiredarray pattern, eliminating the time-consuming and delicate assemblyprocess associated with conventional metal pin microarrays. Thiscost-effective manufacturing process may allow for microarrays that canbe replaced between analysis runs, rather than being cleaned and reused.This can not only reduce test cycle time, but would also reduce thechances of cross-contamination between tests.

The spring material technology also allows for much smaller channelwidths, limited only by the capabilities of the lithography and/orplating processes. For example, while metal pins may have a minimumchannel width of 10 μm, channel spring probes can be readily formed with1 μm channels. In addition, the smaller channel spring probes can bearranged in much denser arrays than can the larger metal pins.

Also, channel spring probes can be fabricated with almost any desiredgeometry, unlike metal pins, which are generally limited to a singlechannel. For example, channel spring probes could be produced having twoor more channels each. Such multi-channel spring probes could be used,for example, to dispense mixtures of different biological or chemicalsolutions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings, where:

FIG. 1 is a perspective view showing a conventional microarrayingsystem;

FIG. 2 is a perspective view showing a conventional DPN system;

FIG. 3(A) is a perspective view showing a microarraying system using achannel spring probe dispensing assembly according to an embodiment ofthe invention;

FIG. 3(B) is a perspective view showing a DPN system using a channelspring probe micropen assembly according to another embodiment of theinvention;

FIG. 3(C) is a perspective view showing a fluidic circuit using channelspring probe fluid interconnects according to another embodiment of thepresent invention;

FIGS. 4(A), 4(B), 4(C), 4(D), 4(E), 4(F), 4(G), 4(H), and 4(I) aresimplified cross-sectional side views showing a general fabricationprocess utilized to produce channel spring probes according to anotherembodiment of the present invention;

FIG. 5(A) is a top view showing a spring mask formed over a springmaterial film during the fabrication process shown in FIG. 4(C)according to another embodiment of the invention;

FIGS. 5(B), 5(C), 5(D), 5(E), 5(F), 5(G), and 5(H) are detail views ofvarious regions of the spring mask shown in FIG. 5(A) according tovarious embodiments of the invention;

FIGS. 6(A), 6(B), and 6(C) are frontal views showing a process forforming a channel on the surface of a spring beam according to anotherembodiment of the invention;

FIG. 7(A) is a perspective view showing a channel spring probe accordingto another embodiment of the invention;

FIG. 7(B) is an enlarged photograph showing an actual channel springprobe array produced in accordance with the fabrication processdescribed with reference to FIGS. 4(A) through 4(I);

FIGS. 8(A), 8(B), 8(C), 8(D), 8(E), and 8(F) are frontal views ofchannel spring probe tips according to various embodiments of theinvention;

FIGS. 8(G), 8(H), and 8(I) are top views of channel spring probe tipsaccording to various embodiments of the invention

FIGS. 9(A), 9(B), and 9(C) are top, cross-sectional side, and end views,respectively showing a channel spring probe incorporating actuationelectrodes according to an embodiment of the present invention; and

FIGS. 10(A), 10(B), and 10(C) are cross-sectional side views depictingactuation of the channel spring probe of FIG. 9(B).

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 3(A) is a perspective view of a microarraying system 300A accordingto an embodiment of the invention. Microarraying system 300A includes astage 310A for supporting an analytical IC 320A, a dispensing assembly330A mounted to a positioning subsystem 370A, and a computer/workstation380A that serves as both a system controller and a measurement dataprocessor. Analytical IC 320A can comprise a biochip or any other typeof IC providing surface-based analysis capabilities. Positioningsubsystem 370A moves dispensing assembly 330A in response to controlsignals provided by computer/workstation 380A to collect and dispensesamples of test solutions in an array pattern on analytical IC 320A.Note that positioning subsystem 370A can perform all the positionaloperations required to dispense the test samples on analytical IC 320A,or stage 310A could also include additional positioning capabilities foraligning analytical IC 320A and dispensing assembly 330A. Once the testsamples have been deposited, analytical IC 320A performs a parallelanalysis and provides the results to computer/workstation 380A forfurther processing. Microarraying system 300A is therefore substantiallysimilar to microarraying system 100 shown in FIG. 1, except that metalpin-based microarray 130 is replaced with channel spring probe-baseddispensing assembly 330A.

Dispensing assembly 330A includes a plurality of channel spring probes350A in an array formation on a substrate 340A. As noted previously,channel spring probes 350A can be produced much more economically thanprinting tips 150 of microarraying system 100, and also can providesignificantly improved accuracy and design flexibility. Each channelspring probe 350A includes a channel 351A that runs parallel to thecurvature of the channel spring probe. Channels 351A are sized such thattest solutions are pulled along the channel by capillary action.Therefore, when any of channel spring probes 350A is placed in contactwith a liquid source, liquid is drawn in to channel 351A. Similarly,when the tip of any of channel spring probes 350A is placed in contactwith the surface of analytical IC 320A, a quantity of liquid fromchannel 351A is deposited on biochip 320A. Between these liquid drawingand dispensing operations, the liquid is held in channel 351A bycapillary and surface tension forces. An optional reservoir 352A formedin line with each channel 351A can increase the fluid storage capacitiesof channel spring probes 350A. Note that while each of channel springprobes 350A is depicted as having a tapered tip and a single channel,channel spring probes in accordance with embodiments of the inventioncan include any number of different tip and channel configurations, aswill be discussed below. For example, each channel 351A in channelspring probes 350A could represent two channels, thereby allowingdispensing assembly 330A to dispense solution mixtures onto analyticalIC 320A.

FIG. 3(B) is a perspective view of a dip pen nanolithography (DPN)system 300B according to another embodiment of the invention. DPN system300B includes a stage 310B for supporting a substrate 320B (such as awafer), a micropen assembly 330B mounted to an XYZ positioning subsystem370B, and a computer/workstation 380B that serves as a systemcontroller. Micropen assembly 330B includes one or more channel springprobes 350B mounted in a mounting base 340B. XYZ positioning subsystem370B moves micropen assembly 330E in response to control signalsprovided by computer/workstation 380B to print a desired pattern onwafer 320B. A channel 351B (parallel to the curvature of channel springprobe 350B) and an optional reservoir 352B in channel spring probe(s)350B allow a print solution to be applied onto wafer 320B. DPN system300B is therefore substantially similar to DPN system 200 shown in FIG.2, except that metal pin-based micropen assembly 230 is replaced withchannel spring probe-based micropen assembly 330B, once again providingthe cost and design benefits associated with channel spring probes.

FIG. 3(C) is a schematic view of a fluidic circuit 300C according toanother embodiment of the invention. Circuit 300C includes fluidicdevices 320C(1) and 320C(2), which can comprise any devices that use orincorporate microfluidic liquid volumes. For example, fluidic devices320C(1) and 320C(2) can comprise biochips or other analytical integratedcircuits (ICs) designed for fluid analysis. Fluidic device 320C(1)includes channel spring probes 350C(1) and 350C(2) for liquid collectionand dispensing, respectively, a micro-channel network 321C for in-planefluid routing, and an optional reservoir 322C for liquid storage. Thefree end of channel spring probe 350C(1) is placed in contact with aliquid 391C in an external supply container 390C, and capillary forcesdraw some of liquid 391C into a channel 351C(1) running parallel to thecurvature of channel spring probe 350C(1). This drawn liquid can eitherbe accumulated in optional reservoir 322C or passed to micro-channelnetwork 321C. Micro-channel network 321C then routes the liquid toappropriate locations within fluidic device 320C(1), including to achannel 351C(2) in channel spring probe 350C(2). Channel 351C(2), whichruns parallel to the curvature of channel spring probe 350C(2), allowsthe liquid to be dispensed from the tip of channel spring probe 350C(2)onto fluidic device 320C(2).

FIGS. 4(A) through 4(I) are simplified cross-sectional side viewsshowing a general fabrication process utilized to produce channel springprobes such as channel spring probes 350A, 350B, and 350C, as shown inFIGS. 3(A), 3(B), and 3(C), respectively, according to anotherembodiment of the present invention.

Referring to FIG. 4(A), the fabrication process begins by forming arelease layer 445 on a wafer 440. Substrate 440 is formed from aselected substrate material (e.g., glass, quartz, silicon (Si),sapphire, aluminum oxide, or a suitable plastic). In one embodiment,release layer 445 includes one or more of Si, a silicon nitridecomposition (SiNx), a silicon oxide composition (SiOx), or titanium (Ti)that is deposited onto substrate 440. As described below, the releasematerial is selected such that the channel spring probe remainsconnected via a portion of release layer 445 to substrate 440 afterrelease. In an alternative embodiment, a separate anchor pad isseparately formed adjacent to the release material that serves toconnect the spring probe to substrate 440. While such a separatelyformed anchor pad may increase the strength of the channel springprobe/substrate connection, the formation of such an anchor pad wouldincrease the number of process steps, thereby increasing the total probemanufacturing cost. In yet another alternative embodiment, the substratematerial of substrate 440 may itself be used as the release layer (i.e.,a separate release material deposition process is not used, and channelspring probe 450 is connected directly to substrate 440, as demonstratedby channel spring probes 350C(1) and 350C(2) in FIG. 3(C)).

Next, as shown in FIG. 4(B), a stress-engineered (spring material) film465 is formed on release layer 445 using known processing techniquessuch that film 465 includes internal stress variations in the growthdirection. For example, in one embodiment, stress-engineered film 465 isformed such that its lowermost portions (i.e., adjacent to releasematerial layer 410) have a higher internal compressive stress than itsupper portions, thereby forming internal stress variations that cause abending bias away from substrate 440. Methods for generating suchinternal stress variations in stress-engineered film 465 are taught, forexample, in U.S. Pat. No. 3,842,189 (depositing two metals havingdifferent internal stresses) and U.S. Pat. No. 5,613,861 (e.g., singlemetal sputtered while varying process parameters), both of which beingincorporated herein by reference. In one embodiment, stress-engineeredfilm 465 includes one or more metals suitable for forming a springstructure (e.g., one or more of molybdenum (Mo), a “moly-chrome” alloy(MoCr), tungsten (W), a titanium-tungsten alloy (Ti:W), chromium (Cr),and nickel (Ni)). In other embodiments, stress-engineered film 465 isformed using Si, nitride, silicon oxide, carbide, or diamond. Thethickness of stress-engineered film 465 is determined in part by theselected spring material, desired spring constant and shape of the finalspring beam structure, as discussed in additional detail below.

Referring to FIGS. 4(C) and 5(A)-5(I), an elongated spring mask 446(e.g., photoresist) is then patterned over selected portions ofstress-engineered film 465. Note that spring mask 446 is formed in theshape of the desired channel spring probe, and may include various tip,channel, and attachment region configurations. The well-characterizedlithography processes that can be used to print spring mask 446 allowfor significant flexibility in the actual geometry of spring mask 446.For example, FIG. 5(A) shows a plan view of spring mask 446, accordingto an embodiment of the invention. Spring mask 446 includes a probe tipregion 446-A at one end, an attachment region 446-B at the other end,and a channel region 446-C between probe tip region 446-A and attachmentregion 446-B. Channel region 446-C is sized such that the resultingchannel formed in the final channel spring probe provides the necessarycapillary action on the liquid being collected by, stored in, ordispensed from the channel spring probe. FIG. 5(A) also indicates arelease region 446-D, the portion of spring mask 446 corresponding tothe portion of the channel spring probe to be released from substrate440.

Note that while channel region 446-C is shown as overlapping with probetip region 446-A, according to other embodiments of the invention,channel region 446-C can also extend into attachment region 446-B. Forexample, FIG. 5(B) shows a channel region 446-C(1) extending throughrelease region 446-D into attachment region 446-B. An optional narrowedregion 447 is included to provide a region of increased flexibility forthe final channel spring probe (note that while narrowed region 447 isdepicted where release region 446-D meets attachment region 446-B forexplanatory purposes, narrowed region 447 can be located anywhere alongrelease region 446-B). Various other modifications can be made tochannel region 446-C, according to the intended usage of the finalspring channel probe. For example, FIG. 5(C) shows a channel region446-C(2) in accordance with another embodiment of the invention. Theinterior end of channel region 446-C(2) is connected to a reservoirregion 520 for creating a reservoir feature in the final channel springprobe. Since the resulting reservoir feature will be wider than thechannel width, the fluid holding capacity of channel region 446-C(2)will be increased. Note that while reservoir region 520 is shown asbeing located in release region 446-D, it can also be positioned inattachment region 446-B, as indicated by the dashed lines.

The invention also allows multiple channels to be formed in a channelspring probe. For example, FIG. 5(D) shows a portion of spring mask 446having channel regions 446-C(3) and 446-C(4), in accordance with anotherembodiment of the invention. Note that like the channel regionsdescribed previously with respect to FIGS. 5(B) and 5(C), channels446-C(3) and 446-C(4) can include reservoir features and/or can extendinto attachment region 446-B, as indicated by the dashed lines.

The same configuration flexibility applies to both attachment region446-B and probe tip region 446-A shown in FIG. 5(A). For example, whiledepicted as a substantially rectangular region in FIGS. 5(A)-5(D),attachment region 446-B can take any number of forms. FIG. 5(E) shows anattachment region 446-B(1), in accordance with another embodiment of theinvention. Attachment region 446-B(1) has the same width as releaseregion 446-D, which will result in a straight-line (i.e., uniform width)channel spring probe having a uniform width. Various other attachmentregion configurations are possible, including, but not limited to,V-shaped, U-shaped, J-shaped, and L-shaped configurations. FIG. 5(F)shows an attachment region 446-B(2) that is enlarged to allow extendedrouting of channel region 446-C(5), thereby allowing both out-of-planeand in-plane fluid routing channels to be formed by a single lithographyprocess step.

Similarly, probe tip region 446-A can take any configuration required toform the desired channel spring probe. For example, FIG. 5(G) shows aprobe tip region 446-A(1) in accordance with another embodiment of theinvention. In contrast to the blunt probe tip region 446-A shown in FIG.5(A), probe tip region 446-A(1) includes chamfers 501 and 502 thatprovide a tapered tip on each side of channel region 446-C. This taperedtip configuration can reduce fluid travel along the (printing) edge ofthe resulting channel spring probe tip, thereby enabling the dispensingof finer fluid lines than would be possible with a similar channelspring probe having a flat tip configuration.

FIG. 5(H) shows a probe tip region 446-A(2), in accordance with anotherembodiment of the invention. Probe tip region 446-A(2) not only includeschamfers 501 and 502, but also includes a pointed tip 505 that closesoff the end of channel region 446-C. By properly sizing pointed tip 505and its distance from the end of channel region 446-C, fluid in theresulting channel spring probe could wick from the channel region to theapex of the sharp pointed tip, thereby allowing extremely fine fluidlines to be dispensed. According to an embodiment of the invention,channel region 446-C can end 1-3 μm or less from the apex of pointed tip505.

Returning to the channel spring probe fabrication process, FIG. 4(D)shows the exposed portions of stress-engineered film 465 surroundingspring mask 446 being etched using one or more etchants 480 to form aspring island 465-1. Note that this etching process is performed suchthat limited etching occurs in release layer 445 surrounding springmaterial island 465-1. In one embodiment, the etching step may beperformed using a wet etch process to remove exposed portions ofstress-engineered film 465—e.g., the use of a cerric ammonium nitratesolution to remove a MoCr spring metal layer. In another embodiment,anisotropic dry etching is used to etch both stress-engineered film 465and the upper surface of the exposed portion of release layer 445. Thisembodiment may be performed, for example, with Mo spring metal, and Sior Ti release layers. Mo, Si and Ti all etch in reactive fluorineplasmas. An advantage of dry etching the spring material film is that itfacilitates finer features and sharper tipped channel spring probes.Materials that do not etch in reactive plasmas may still be etchedanisotropically by physical ion etching methods, such as argon ionmilling. In yet another possible embodiment, the etching step can beperformed using the electro-chemical etching process described in IBM J.Res. Dev. Vol. 42, No. 4, page 655 (Sep. 4, 1998), which is incorporatedherein by reference. Many additional process variations and materialsubstitutions are therefore possible and the examples given are notintended to be limiting.

FIG. 4(E) shows spring material island 465-1 and release layer 445 afterspring mask 446 (FIG. 4(D)) is removed. At this point, optional channelarea patterning 466 may be formed on spring material island 465-1, asindicated in FIG. 4(F). Channel area patterning 466 allows secondarychannel features to be formed on spring material island 465-1. Note thatif channel features have already been patterned into spring island465-1, optional channel area patterning 466 would not be required,although secondary channel features could be used to modify or add tothe features integrated into spring island 465-1. Note further that thisadditional channel area patterning can alternatively be performed afterthe appropriate portion of spring material island 465-1 is released fromsubstrate 440 (to be discussed with respect to FIG. 4(H)).

In FIG. 4(G), a release mask 450 is formed on a first portion 465-1A ofspring material island 465-1. Release mask 491 defines a release windowRW, which exposes a second portion 465-1B of spring material island465-1 and surrounding portions release layer 445. Release mask 491 mayalso serve as a strapping structure to further secure first portion465-1A to substrate 440. In one embodiment of the invention, releasemask 491 is formed using photoresist. In other embodiments of theinvention, a suitable metal or epoxy may be used. Note that according toother embodiments of the invention, release mask 491 could be eliminatedthrough appropriate patterning of release layer 445 and/or first portion465-1A of spring material island 465-1.

At this point, substrate 440 can be diced (for example along dice linesDL1 and DL2) to prevent damage to the subsequently lifted structures(i.e., spring beam 460 shown in FIG. 4(H)). An optional sticky dicingtape 441 could be used to prevent shifting of the substrate during andafter dicing (i.e., the dicing blade only cuts through substrate 440(and the overlying portions of release layer 445) but not through theunderlying sticky tape 441). Alternatively, dicing could be performedafter release of portion 465-1B from substrate 440. In such a case, ifprotection of the released beams during dicing were desired, beampassivation using resist or wax could be used.

In FIG. 4(H), a release etchant 481 (e.g., a buffered oxide etch) isused to selectively remove a portion of release layer 445 from beneaththe exposed portion of spring island 465-1 (i.e., second portion 465-1B)and foLm a curved spring beam 460. Specifically, removal of the exposedrelease material causes cantilever portion 454 of spring beam 460 tocurve away from substrate 440 in response to the internal stressvariations established during the formation of the stress engineeredfilm (discussed above). Note that fixed end 453 of spring beam 460remains secured to substrate 440 by release material (support) portion445A, which is protected by release mask 491. Alternatively, releasemask 491 may be removed from fixed end 453 of spring beam 460 afterrelease. Optional channel area patterning 466 can be formed on springbeam 460 at this point (i.e., after release) if it has not beenpreviously formed (e.g., in FIG. 4(F)). Then, if channel area patterning466 is present, additional deposition process(es) can be performed toform the actual channel structure 467 of the completed channel springprobe 450 shown in FIG. 4(I) (as noted previously, the channel featurescould be defined within (i.e., integrated into) spring beam 460, inwhich case spring probe 450 would not require channel structure 467).

The formation of channel structure 467 is demonstrated in greater detailin FIGS. 6(A)-6(C). FIG. 6(A) shows a frontal (head-on) view ofintermediate probe tip 455 shown in FIG. 4(H), with channel areapatterning 466 overlying a desired portion of spring beam 460. Channelarea patterning 466 can comprise a hard mask (e.g., hard resist) or anyother material that can be removed without removing the subsequentlyfoamed channel structure. In FIG. 6(B), channel structure 467 is formedon the portions of spring beam 460 not masked by channel area patterning466, and a resist strip 482 is applied to remove channel area patterning466. A frontal view of the resulting probe tip 456 (from FIG. 4(I)) isshown in FIG. 6(C), with the gap formerly occupied by channel areapatterning 466 becoming channel 468. Note that various other geometriesfor channel area patterning 466 and channel structure 467 are possible,as will be described with respect to FIGS. 8(B)-8(H). According to anembodiment of the invention, channel structure 467 can be electroplatedonto spring beam 460. According to other embodiments of the invention,various other materials (e.g., oxides, nitrides, organic materials(carbides), etc.) and processes (e.g., sputtering, evaporation, chemicalvapor deposition (CVD), spinning, etc.) can be used to form channelstructure 467. Note that channel structure (467) can be formed prior tothe release of spring beam 460 from substrate 440 (i.e., on springisland 465-1 shown in FIG. 4(G)), although the channel structure wouldgenerate beam loading that could reduce the release height of springbeam 460.

Returning to FIG. 4(I), according to an embodiment of the invention,substrate 440 can include integrated fluidic paths, as indicated byoptional fluidic path 444. Channel spring beams can be formed on asubstrate that already includes such integrated fluidic paths tosimplify the construction of advanced fluidic routing systems. Forexample, an optional support structure 442 can be attached to substrate440 to provide additional mechanical support and/or interface elements.Support structure 442 can include an optional fluid reservoir 443 forsupplying channel spring probe 450 with liquid. In such a situation,substrate 440 could include a preformed integrated via (fluidic path444), that would couple the channel of channel spring probe 450 withreservoir 443 of support structure 442. Fluid reservoir 443 could theneither supply liquid to, or store liquid gathered by, spring channelprobe 450.

According to another embodiment of the invention, an optional protectivecoating 461 (indicated by a dotted line) such as paralyne or oxide canalso be formed over any exposed portions of spring beam 460 (and channelstructure 467). According to another embodiment of the invention, anoptional secondary tip 469 can be formed at, or attached to, the end ofspring beam 460 using methods like FIB, EBD, carbon-nanotube growth, byetching a material deposited on the surface of spring beam 460 prior torelease, or by post-release attachment. Various secondary tipconfigurations are described more fully in co-owned, co-pending U.S.patent application Ser. No. 10/136,258 entitled “Scanning Probe Systemwith Spring Probe And Actuation/Sensing Structure filed Apr. 30, 2002 byThomas Hantschel et al., herein incorporated by reference.

FIG. 7(A) shows a perspective view of completed channel spring probe 450from FIG. 4(I). Channel spring probe 450 can now be used in any fluidicsystem, such as microarraying system 300A shown in FIG. 3(A), DPN system300B shown in FIG. 3(B), and fluidic circuit 300C shown in FIG. 3(C).Note that channel spring probe 450 also includes optional operationalmodules 495 that can be formed after or in conjunction with the processdescribed with respect to FIGS. 4(A)-4(I). Operational modules can beadjacent to or attached to spring beam 460, and can comprise variousstructures for providing additional functionality to channel springprobe 450, such as actuators, heaters, temperature sensors, stresssensors, optical detectors, deflection sensors, chemical sensors, andintegrated electronic circuits (for controlling actuation, signalprocessing, etc.). For example, each of the channel spring probes in anarray of channel spring probes (such as microarray 330A shown in FIG.3(A) or micropen assembly 330B shown in FIG. 3(B)) can include anactuator and a deflection sensor to help align the tips of all thechannel spring probes.

For example, FIGS. 9(A) through 9(C) are top, cross-sectional side, andend views, respectively, showing a channel spring probe 950incorporating an actuation electrode structure including a firstelongated electrode portion 995(A) and a second elongated electrodeportion 995(B) formed on substrate 940 and extending parallel to andoffset from the sides of spring beam 960. Each of elongated electrodeportions 995(A) and 995(B) has a tapered shape including a relativelywide portion 996 located adjacent to fixed end 953 of spring beam 960,and a relatively narrow portion 997 located adjacent to probe tip 956.The present inventors have determined that tapered electrode portions995(A) and 995(B) reduce forces exerted along the length of spring beam960 due to the diminished field strength (along its length) inherent tothe tapered electrode design, thereby facilitating a stable“rolling/zipper” motion of spring beam 960 (described below withreference to FIGS. 10(A) through 10(C). Further, by offsetting taperedelectrode portions 995(A) and 995(B) from (i.e., mounting on oppositesides of) spring beam 960, the actuation voltage needed to achieve fulldeflection of probe tip 956 is minimized. Other electrostatic actuationelectrode patterns are described in co-owned, co-pending U.S. patentapplication Ser. No. 10/136,258 entitled “Scanning Probe System withSpring Probe And Actuation/Sensing Structure filed Apr. 30, 2002 byThomas Hantschel et al. Note that spring beam 960 can also includes anoptional narrowed portion 947, as indicated in FIG. 9(A), to reduce theforce required to deflect spring beam 960. Alternatively, spring beam960 can include an enhanced flexibility portion 948, as indicated inFIG. 9(B) to provide a similar effect. Note further that enhancedflexibility portion 948 can be formed in various ways, including locallythinning spring beam 960 or locally integrating a softer material intospring beam 960. Note further that narrowed portion 947 in FIG. 9(A) andenhanced flexibility portion 948 in FIG. 9(B) can be located anywherealong cantilever portion 954.

FIGS. 10(A) through 10(C) are cross-sectional side views illustratingthe “rolling/zipper” motion of spring beam 960. Referring to FIG. 4(A),when a relatively small voltage signal is applied by a voltage source901 to spring beam 960 and elongated electrode portions 995(A) and995(B), cantilever portion 954 remains substantially in its unbiasedposition (i.e., bent into a shape determined by the channel spring probedesign). As shown in FIG. 10(B), as the applied voltage generated byvoltage source 901 increases, cantilever portion 954 is actuated towardssubstrate 940 and straightened, thereby “unrolling” spring beam 960. Asshown in FIG. 10(C), when the applied voltage generated by voltagesource 901 reaches a sufficiently large value, spring beam 960 isfurther unrolled until tip 956 abuts substrate 940. This actuationcapability can substantially improve the functionality of devicesincorporating channel spring probes. For example, in microarray 330Ashown in FIG. 3(A), individual channel spring probes 350A can be “turnedoff” by actuating them towards substrate 340A. In a similar manner,individual channel spring probes in micropen assembly 330B shown in FIG.3(B) can be turned off and on via actuation towards (and away from)substrate 340B.

FIG. 7(B) is an enlarged photograph showing an actual channel springprobe array 730 that was produced by the present inventors utilizing thefabrication process described above. Channel spring probe array 730includes channel spring probes 750(1), 750(2), 750(3), and 750(4) (amongothers not labeled for clarity) curving away from a substrate 740. Eachof channel spring probes 750(1)-750(4) is attached to substrate 740 at afixed end 753 and includes a channel as previously described withrespect to FIG. 7(A). For example, channel spring probe 750(1) includesa channel 752 that extends completely through a tapered probe tip 756(such as defined by probe tip region 446-A(1), described with respect toFIG. 5(H)). Note also that channel 752 extends into fixed end 753 andends in a reservoir 753, as was previously described with respect toFIGS. 5(B) and 5(C).

Returning to FIG. 7(A), note that channel 452 in spring beam 460includes a channel 452 that could be supplemented or replaced by channelfeatures in optional channel structure 467 (shown simply as a dashedvolume for clarity). Therefore, probe tip 456 can take a variety offorms. For example, FIG. 8(A) shows a frontal view of a probe tip 456(1)in accordance with an embodiment of the invention. Probe tip 456(1)includes a channel 452(1) defined by both spring beam 460 and channelstructure 467(1). Channel structure portions 467(1)-A and 467(1)-B arepositioned directly over spring beam portions 460-A and 460-B,respectively, thereby increasing the height of the channel included inspring beam 460.

FIG. 8(B) shows a frontal view of a probe tip 456(2) in accordance withanother embodiment of the invention. Rather than adding to an existingchannel in the spring beam, channel structure 467(2) in probe tip 456(2)is formed on a spring beam 460(1) that does not include any channelfeature (i.e., a “blank” spring beam). A channel 468(1) is thereforedefined entirely by channel structure portions 467(2)-A and 467(2)-B.

FIG. 8(C) shows a frontal view of a probe tip 456(3) in accordance withanother embodiment of the invention. In probe tip 456(3), channelstructure 467(3) formed on blank spring beam 460(1) defines a fullyenclosed channel 468(2). Channel structure 467(3) could be formed, forexample, by completely plating over channel area patterning such asshown in FIG. 6(A). Since channel 468(2) is enclosed on all sides, fluidaccess/egress is only possible through the ends of channel 468(2), whichcan minimize the risks of fluid contamination and provide more securetransport for liquids held in channel 468(2).

FIG. 8(D) shows a frontal view of a probe tip 456(4) in accordance withanother embodiment of the invention. Channel structure 467(4) defineschannels 468(3) and 468(4) by positioning channel structure portions467(4)-A, 467(4)-B, and 467(4)-C on blank spring beam 460(1). Note thatthis principle may be used to form any number of channels in a channelspring probe.

FIG. 8(E) shows a frontal view of a probe tip 456(5) that includesmultiple channels in accordance with another embodiment of theinvention. Probe tip 456(5) includes channel structures 467(5) and467(6) on the top and bottom surfaces, respectively, of blank springbeam 460(1). Channel structure 467(5) includes channel structureportions 467(5)-A and 467(5)-B that define a channel 468(5) on the topsurface of spring beam 460(1), while channel structure 467(6) includeschannel structure portions 467(6)-A and 467(6)-B that define a channel468(6) on the bottom surface of spring beam 460(1). Note that probe tip456(5) could include only channel structure 467(6) (as indicated by thedashed lines used for channel structure 467(5)), thereby providing achannel (i.e., channel 468(6)) on only the bottom surface of spring beam460(1).

FIG. 8(F) shows a frontal view of a probe tip 456(6) that includesmultiple enclosed channels in accordance with another embodiment of theinvention. Probe tip 456(6) includes channel structures 467(7) and467(8) on the top and bottom surfaces, respectively, of blank springbeam 460(1), thereby defining fully enclosed channels 468(7) and 468(8),respectively. Note that probe tip 456(6) could include only channelstructure 467(8) (as indicated by the dashed lines used for channelstructure 467(7)), thereby defining a channel (i.e., channel 468(8)) ononly the bottom surface of spring beam 460(1).

Note that channel features created by the aforementioned types ofchannel structures can include any reservoir features (such as thosedescribed with respect to FIGS. 5(C) and 5(D)) or other formations thatare desired on the surface of the spring beam. For example, FIG. 8(G)shows a plan view of a probe tip 456(7) in accordance with anotherembodiment of the invention. Probe tip 456(7) includes channel structureportions 467(9)-A through 467(9)-H, arranged on blank spring beam 460(1)to define a channel 468(9) and cross channels 469-A, 469-B, and 469-C.Cross channels 469-A, 469-B, and 469-C are perpendicular to channel468(9) and span the width of spring beam 460(1). Channel structureportions 467(9)-A and 467(9)-E are angled such that probe tip 467(7) hasa substantially tapered end. Such a configuration can, for example, beused in puncture applications, with cross channels 469-A, 469-B, and469-C providing increased fluid delivery capacity. FIG. 8(H) provides aside view of probe tip 456(7), showing cross channels 469-A, 469-B, and469-C spaced along the surface of spring beam 460(1).

FIG. 8(H) shows a plan view of a probe tip 456(8) having cross channelsin accordance with another embodiment of the invention. Probe tip 456(8)is substantially similar to probe tip 456(7) shown in FIGS. 8(G) and8(H), except that channel structure portions 467(9)-A and 467(9)-E inprobe tip 456(7) are replaced with a single channel structure portion467(9)-I that includes a pointed tip 467(9)-J. Pointed tip 467(9)-Jcloses off channel 468(10) at the end of probe tip 456(8). As describedpreviously with respect to FIG. 5(H), pointed tip 467(9)-J can stillallow fluid transport to and from channel 468(10), while providingadditional stability and piercing capability to probe tip 456(8).

Although the present invention has been described in connection withseveral embodiments, it is understood that this invention is not limitedto the embodiments disclosed, but is capable of various modificationsthat would be apparent to one of ordinary skill in the art. For example,a spring beam (or even a bond wire, such as produced by FormFactor,Inc.) could be plated on all sides and then etched away, leaving onlythe plating as an out-of-plane tube. Thus, the invention is limited onlyby the following claims.

1. A method for forming a fluidic conduit, the method comprising:forming a plurality of spring material islands in an array pattern on arelease material layer such that each of the plurality of springmaterial islands has an internal stress gradient in a direction normalto the release material layer; removing a first portion of the releasematerial layer from beneath a cantilever portion of the spring materialisland, thereby causing the cantilever portion to assume a curvaturebending away from a second portion of the release layer due to theinternal stress gradient; and defining a first channel for carryingfluid along the cantilever portion of the spring beam, the first channelrunning substantially parallel to the curvature of the cantileverportion.
 2. The method of claim 1, further comprising masking a fixedend portion of the spring material island.
 3. The method of claim 1,further comprising depositing said release material layer on asubstrate, wherein the release material layer comprises one or more ofsilicon (Si), silicon-nitride (SiNx), silicon-oxide (SiOx), and titanium(Ti).
 4. The method of claim 1, wherein forming the plurality of springmaterial islands in an array pattern comprises: forming a springmaterial film on the release material layer, the spring material filmhaving the internal stress gradient in a direction normal to the releasematerial layer; and etching the spring material film to form theplurality of spring material islands in an array pattern.
 5. The methodof claim 4, wherein forming the spring material film comprisessputtering the spring material film on a wafer formed from the releasematerial.
 6. The method of claim 4, wherein forming the spring materialfilm comprises sputtering one or more metals selected from molybdenum(Mo), tungsten (W), titanium (Ti), chromium (Cr), and nickel (Ni) whilealtering process parameters such that portions located adjacent to therelease material layer have a higher internal compressive stress thanportions located further from the release material layer.
 7. The methodof claim 4, wherein etching the spring material film comprises: forminga first mask on the spring material film; and etching exposed portionsof the spring material film located around the first mask.
 8. The methodof claim 7, wherein defining the first channel comprises including afirst elongated slot in the first mask such that the spring materialisland includes a first in-plane channel feature in the cantileverportion, the first in-plane channel feature being substantially parallelto the cantilever portion, the first in-plane channel feature becomingthe first channel after the removal of the release material layer frombeneath the unmasked cantilever portion of the spring material island.9. The method of claim 8, wherein the first mask includes a tapered endsuch that the spring material island includes an in-plane tapered tipshaped by the tapered end.
 10. The method of claim 9, wherein the firstelongated slot extends completely through the tapered end.
 11. Themethod of claim 9, wherein the tapered end terminates in a pointed tip,and wherein the first elongated slot extends into the tapered end andends before the pointed tip.
 12. The method of claim 8, wherein thefirst in-plane channel feature extends into the fixed end portion of thespring material island.
 13. The method of claim 8, further comprisingdefining a second channel for carrying fluid along the cantileverportion of the spring beam, the second channel running substantiallyparallel to the curvature of the cantilever portion, wherein definingthe second channel comprises including a second elongated slot in thefirst mask such that the spring material island includes a secondin-plane channel feature in the cantilever portion, the second in-planechannel feature being substantially parallel to the cantilever portion,wherein after removal of the release material layer from beneath theunmasked cantilever portion of the spring material island, the secondin-plane channel feature becomes the second channel.
 14. The method ofclaim 1, wherein defining the first channel comprises: forming a firstchannel structure pattern on a first surface of the cantilever portion,the first channel structure pattern covering a first channel portion onthe first surface of the cantilever portion; depositing channelstructuring material on exposed portions of the first surface locatedaround the first channel portion; and removing the first channelstructure pattern, thereby revealing the first channel.
 15. The methodof claim 14, wherein the first channel structure pattern comprises ahard resist, and wherein removing the first channel structure patterncomprises applying a resist strip.
 16. The method of claim 14, whereindepositing channel structuring material comprises forming a metalplating on the cantilever portion.
 17. The method of claim 14, whereinthe channel structuring material covers the first channel portion. 18.The method of claim 14, further comprising defining a second channel forcarrying fluid along the cantilever portion of the spring beam, thesecond channel running substantially parallel to the curvature of thecantilever portion, wherein defining the second channel comprises:forming a second channel structure pattern on the first surface of thecantilever portion, the second channel structure pattern covering asecond channel portion on the first surface of the cantilever portion;depositing channel structuring material on exposed portions of the firstsurface located around the second channel portion; and removing thesecond channel structure pattern, thereby revealing the second channel.19. The method of claim 14, further comprising defining a second channelfor carrying fluid along the cantilever portion of the spring beam, thesecond channel running substantially parallel to the curvature of thecantilever portion, wherein defining the second channel comprises:forming a second channel structure pattern on a second surface of thecantilever portion, the second channel structure pattern covering asecond channel portion on the first surface of the cantilever portion,the first surface of the cantilever portion facing away from the releasematerial layer and the second surface of the cantilever portion facingtowards the release material layer; depositing channel structuringmaterial on exposed portions of the second surface located around thesecond channel portion; and removing the second channel structurepattern, thereby revealing the second channel.